I've never really messed with .avi in Poser but this problem seems to pop up fairly frequently. I don't know whether Poser is especially picky about codecs or what.

Get GSpot http://www.headbands.com/gspot/ It will tell you which video/audio codec an avi is using. If you have a clip that does work in Poser, you'll be able to see which codec works.

VirtualDub is great but I also use Avidemux http://fixounet.free.fr/avidemux/ for simple editing and transcoding (conversion).

You might also try Sherlock the Codec Detective. It was built for XP but is supposed to work on Vista. Maybe it will workk on Win7. It gives you details about the codecs installed on your system and their status i.e. if one is broken.

http://www.updatexp.com/sherlock-codec-detective.html

 

Hope that helps. 

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